1. Field of the Invention
The present invention relates to low viscosity graft polymer dispersions in a mixture of polyols. More particularly, the invention relates to graft polymer dispersions prepared by the free radical polymerization of an ethylenically unsaturated monomer or mixture of monomers in a polyol mixture comprising (1) from about 25 to about 99 weight percent of a polyol containing from 2 to 8 hydroxyl groups and an equivalent weight from 30 to about 200 and (2) from about 1 to about 75 weight percent of a macromer containing induced unsaturation, the macromer being the reaction product of a polyether polyol and a compound having both ethylene unsaturation and a group selected from the group consisting of a hydroxyl, carboxyl, anhydride, isocyanate and epoxy group.
2. Description of the Prior Art
The prior art, as evidenced by U.S. Pat. Nos. 3,652,658; 3,875,258; 3,950,317, and Reissue U.S. Pat. Nos. 28,715 and 29,014 teaches the preparation of graft polymer dispersions which are useful in the preparation of polyurethanes by the polymerization of ethylenically unsaturated monomers in polyols. The above patents disclose various methods of preparing graft polymer dispersions. U.S. Pat. No. 3,931,092 teaches the preparation of polymeric solids by carrying out the polymerization in the presence of a free-radical initiator and an organic solvent. The solvent concentration employed is from about 1 part to 19 parts by weight per part of the hydroxy-terminated organic compound which has a polymerizable carbon double bond. U.S. Pat. No. 3,953,393 teaches the preparation of graft copolymer dispersions by employing alkylmercaptan chain transfer agents at concentrations from 0.1 to 2 percent by weight based on the weight of vinyl monomer.
Stable dispersions of polymers in polyols have found broad commercial use in the preparation of polyurethanes. The use of these dispersions, known in the trade as graft or polymer polyols, improves processing and, among other properties, the firmness of the polyurethane products, often expressed as load bearing or modulus. There have been many attempts to improve the products representing the present state of the art. Efforts have been directed towards increasing the amount of polymer which is dispersed in the polyol, the obvious benefit being that firmer polyurethanes can be produced.
The prior art has not taught that in situ free radical polymerizations may be conducted in a polyol mixture comprising (1) from about 25 to about 99 weight percent of a polyol containing from 2 to 8 hydroxyl groups and an equivalent weight from 30 to about 200 and (2) from about 1 to about 75 weight percent of a macromer containing induced unsaturation, the macromer being the reaction product of a polyether polyol and a compound having both ethylene unsaturation and a group selected from the group consisting of a hydroxyl, carboxyl, anhydride, isocyanate and epoxy group.